never understood drilling the air box thing
I would only ever cut a large hole to fit a cold air feed, but not drill the air box as you are trying to keep the hot air from the engine bay away from the air box, therefore dilling holes allows an aspect of hot air to be sucked in
Smoothing the air box may not make a massive amount of difference, but think about how air travels and why aerodynamics are important? the smoother the inside of the airbox, the quicker air can travel over a surface, and the quicker the air can travel over a surface, the theory is that more air enters into the intake. Basically les disruption to the flow of air, aiding for overall improvement to g/s